The energy return on energy invested (EROEI) is just a measure of “bang for your buck.” It tells you how much energy you deliver relative to how much energy it took to deliver it. Let’s say running a drilling rig takes a gallon of fuel. The oil extraction pump takes another gallon. Plus, the delivery truck takes another gallon (I’m simplifying). That’s three gallons of fuel to deliver fuel to the station. If that truck delivers 12 gallons, then the EROEI is 4:1.
Back in 1962 when the Beverly Hillbillies debuted, the EROEI on oil was about 10. In the opening for that show, Jed Clampett accidentally strikes oil with an errant gunshot. It bubbles out of the ground for free. That kind of oil has a very high EROEI (very little drilling or pumping, and its location requires less transport than, e.g. Prudoe Bay). Oil with very high EROEI is part of the American Mythology. Back in 1940, the EROEI for American oil was over 200. Today it’s closer to 5.
People die mining coal. People die drilling oil. Those fuels make a huge amount of pollution. I’m not even talking about CO2. Why did we tolerate a dangerous, polluting energy source? Because those energy sources used to have the biggest EROEI. The EROEI of coal electricity was about 9 in 2009 (in some cases closer to 3 depending on source and pollution reduction strategies). As we dig deeper to get coal, the EROEI necessarily decreases.
So, if some other energy source has a better EROEI than fossil, it wins. Economics follows thermodynamics. The efficiency of PV systems has increased and production methods have become more refined. Where conditions are favorable, the EROEI of solar PV has passed 8 and is rapidly approaching 10. Solar Technology is getting better continuously. Fossil fuels are getting harder to extract. In the longer term, solar will eat their lunch.